Wireless ic device

ABSTRACT

An electromagnetic coupling module includes a wireless IC chip and a functional substrate. The electromagnetic coupling module is mounted on a radiation plate, preferably using an adhesive, for example. On the upper surface of a base material of the radiation plate, two long radiation electrodes are provided. On the undersurface of the functional substrate, capacitive coupling electrodes that individually face inner ends of the radiation electrodes are provided. A matching circuit arranged to perform the impedance matching between the wireless IC chip and each of the radiation electrodes includes the capacitive coupling electrodes. As a result, it is possible to reduce the size, facilitate the design, and reduce the cost of a wireless IC device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless IC device used for an RFID (Radio Frequency Identification) system for performing wireless data communication using electromagnetic waves.

2. Description of the Related Art

Recently, as a product management system, an RFID system has been used in which a reader/writer arranged to generate an induction field communicates with a wireless IC device attached to a product in a wireless manner so as to obtain predetermined information stored in the wireless IC device.

FIG. 1 is a diagram illustrating an example of a wireless IC tag (RFID tag) disclosed in Japanese Unexamined Patent Application Publication No. 2005-244778 in which an IC tag label is attached to an IC tag antenna.

In a wireless IC tag TO, a pair of main antenna elements 81, an auxiliary antenna element 82, and a pair of matching portions 83 are provided on the surface of a dielectric substrate 84.

The main antenna elements 81 are meandering antennas in which meandering conducting lines are provided, and are symmetrically arranged on the dielectric substrate 84. Between the main antenna elements 81 occupying areas at both ends of the dielectric substrate 84, the auxiliary antenna element 82 is disposed.

The matching portions 83 are meandering conducting lines (inductors). One end of each of the matching portions 83 is individually connected to an inner end of the main antenna elements 81, and the other end of each of the matching portions 83 is connected to a wireless IC chip 86.

However, the wireless IC tag disclosed in Japanese Unexamined Patent Application Publication No. 2005-244778 has the following problems. Since the matching portions are individually arranged adjacent to the main antennas on the same substrate, the size of the wireless tag is increased.

If the tag is attached to a product having a high dielectric constant, the frequency characteristics of the matching circuit portions are changed due to the influence of the dielectric constant of the product. Accordingly, the frequency characteristic of the tag is significantly changed. If a protection film arranged to cover the surface of a product to which the tag is attached or the surface of the tag, the impedances of the matching portions are changed. Accordingly, it is necessary to design the wireless tag in consideration of the use condition of the wireless tag.

Since the auxiliary antenna is used to increase the design flexibility of the main antenna elements, the size of the tag is increased. Since matching design is performed at portions other than the matching portions, the number of design parameters is increased and the design complexity of the tag is increased.

Since the IC chip must be mounted on a small mounting electrode on a large substrate on which the main antennas and the matching portions are disposed, a high-precision mounting apparatus is required. Since the mounting position adjustment requires a long period of time and the manufacturing time for the tag therefore is increased, the cost of the tag is increased.

Since each of the main antennas is connected to the IC chip so that the DC continuity between them is achieved, static electricity may flow from the main antenna into the wireless IC chip and break the wireless IC chip.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention reduce the size and cost of a wireless IC device and facilitate the design of the wireless IC device.

A wireless IC device according to a preferred embodiment of the present includes a wireless IC chip, a radiation plate including a radiation electrode, and a functional substrate including an external coupling electrode coupled to the radiation electrode and a matching circuit arranged to perform impedance matching between the wireless IC chip and the radiation electrode. The matching circuit included in the functional substrate is determined such that a relationship between a reactance component of an impedance obtained by viewing the wireless IC chip from a connecting portion connecting the wireless IC chip and the functional substrate to each other and a reactance component of an impedance obtained by viewing the radiation electrode from the connecting portion connecting the wireless IC chip and the functional substrate to each other is a conjugate relationship.

The external coupling electrode is preferably electromagnetically coupled to the radiation electrode. The functional substrate preferably includes a multilayer substrate including laminated dielectric layers on which electrode patterns are provided.

The radiation electrode is preferably relatively long. The external coupling electrode preferably includes first and second external coupling electrodes that individually occupy two areas divided from the functional substrate. One of two ends of the radiation electrode is preferably coupled to the first external coupling electrode and the other one of the two ends of the radiation electrode is preferably coupled to the second external coupling electrode.

The radiation electrode is preferably a loop-shaped radiation electrode having two ends that face each other. One of the ends is preferably coupled to the first external coupling electrode. The other one of the ends is preferably coupled to the second external coupling electrode.

An auxiliary matching circuit portion preferably includes a matching electrode arranged to connect a location near one of the two ends of the radiation electrode to a location near the other one of the two ends of the radiation electrode, a portion of the radiation electrode from one of the two ends to the location near one of the two ends, and to connect a portion of the radiation electrode from the other one of the two ends to the position near the other one of the two ends.

The inductance elements are preferably loop-shaped inductance elements. Winding axes of the loop-shaped inductance elements are arranged so that they cross an area in which the radiation electrode is provided.

The external coupling electrode is preferably a capacitive coupling electrode that faces the radiation electrode and is capacitively coupled to the radiation electrode.

The capacitive coupling electrode is preferably disposed on a surface of the functional substrate facing the radiation plate. The radiation electrode is preferably disposed on a surface of the radiation plate facing the functional substrate. The functional substrate is preferably attached to the radiation plate so that the capacitive coupling electrode and the radiation electrode face each other.

The external coupling electrode included in the functional substrate preferably extends to a surface other than the surface of the functional substrate facing the radiation plate.

The external coupling electrode is preferably a loop-shaped external coupling electrode. The loop-shaped external coupling electrode is magnetically coupled to the radiation electrode.

At least one of the inductance elements preferably has a double helix shape in which two different linear electrodes are adjacent to each other. One end of one of the two different linear electrodes is preferably electrically connected to one end of the other one of the two different linear electrodes.

The radiation electrode preferably is a loop-shaped radiation electrode. The loop-shaped radiation electrode is preferably electromagnetically coupled to the inductance elements included in the functional substrate.

The matching circuit is preferably defined by an element included in the functional substrate and an element mounted on the functional substrate.

At least one of the wireless IC chip, the functional substrate, and the radiation plate is preferably covered with a protection film.

According to various preferred embodiments of the present invention, the following advantages are obtained. Since the wireless IC chip is mounted on the small functional substrate, it is possible to use an IC mounting apparatus in the related art and reduce the cost of mounting the wireless IC chip. Even if a wireless IC chip having a different output impedance is used and an RFID frequency characteristic is changed, it is only necessary to change the design of the matching circuit included in the functional substrate. This significantly reduces design costs.

Since the wireless IC chip and the functional substrate are DC-insulated from the radiation electrode, it is possible to prevent the wireless IC chip and the functional substrate from being broken by static electricity and improve the resistance of the wireless IC device to static electricity.

Since the inductance elements and/or the capacitance element are included in the multilayer substrate, it is possible to stabilize an inductance value and a capacitance value and reduce the change in impedance caused by an external factor, such as a protection film or an attachment product. Accordingly, it is not necessary to change the design of the wireless IC device in consideration of the dielectric constant of a product attached to the wireless IC device.

The first and second external coupling electrodes that individually occupy two areas divided from the functional substrate are provided, one of two ends of the long radiation electrode faces the first external coupling electrode, and the other one of the two ends of the long radiation electrode faces the second external coupling electrode. As a result, it is possible to easily supply electric power to the radiation electrode.

The radiation electrode is a loop-shaped radiation electrode in which both ends face each other, one of the ends is coupled to the first external coupling electrode, and the other one of the ends is coupled to the second external coupling electrode. As a result, a wireless IC device can perform communication using a magnetic field, is not significantly affected by the dielectric constant of an attachment product, and can obtain a more stable characteristic.

An auxiliary matching circuit portion is defined by a matching electrode arranged to connect a location near one of the two ends of the radiation electrode to a location near the other one of the two ends of the radiation electrode, a portion of the radiation electrode from one of the two ends to the location near one of the two ends, and a portion of the radiation electrode from the other one of the two ends to the location near the other one of the two ends. As a result, the impedance matching between the functional substrate and the radiation plate is performed twice. Therefore, it is possible to maintain a state in which the impedance matching between the functional substrate and the radiation plate is achieved in a wide frequency band, that is, to obtain a high gain in a wide frequency band.

The inductance elements are preferably loop-shaped inductance elements, and winding axes of the loop-shaped inductance elements are preferably arranged so that they cross an area in which the radiation electrode is disposed. As a result, magnetic fields are generated at the loop-shaped inductance elements in a direction that is parallel or substantially parallel to the winding axes of the loop-shaped inductance elements and is vertical or substantially vertical to the radiation electrode. Furthermore, a magnetic field is generated around the radiation electrode, since the radiation electrode is a planar electrode provided on a base material. Accordingly, the magnetic field loop generated at the functional substrate and the magnetic field loop generated at the radiation electrode are interlinked with each other. This strengthens the degree of coupling between the inductance elements and the radiation electrode.

Preferably, the external coupling electrode is a capacitive coupling electrode that is capacitively coupled to the radiation electrode. As a result, it is possible to strengthen the degree of coupling between the external coupling electrode and the radiation electrode. Furthermore, it is possible to simplify the shapes of the external coupling electrode and the radiation electrode and reduce the cost of the wireless IC device.

Preferably, the capacitive coupling electrode is provided on a surface of the functional substrate facing the radiation plate, the radiation electrode is arranged on a surface of the radiation plate facing the functional substrate, and the functional substrate is attached to the radiation plate so that the capacitive coupling electrode and the radiation electrode face each other. As a result, the gap between the capacitive coupling electrode and the radiation electrode is reduced, and the capacitance generated at the gap is increased. This strengthens the degree of coupling between the capacitive coupling electrode and the radiation electrode.

Preferably, the external coupling electrode included in the functional substrate extends to a surface other than the surface of the functional substrate facing the radiation plate. As a result, if the external coupling electrode is connected to the radiation electrode via a conductive joining material, such as solder, it is possible to strengthen the connection between the external coupling electrode and the radiation electrode and increase the impact residence of the wireless IC device.

Preferably, the external coupling electrode is a loop-shaped external coupling electrode, and a magnetic field of the loop-shaped external coupling electrode is coupled to a magnetic field of the radiation electrode. As a result, it is possible to mount the functional substrate on the radiation plate in any suitable orientation. Furthermore, it is possible to reduce the influence of the dielectric constant of a joining material used to connect the functional substrate and the radiation plate.

Preferably, at least one of the inductance elements has a double helix shape in which two different linear electrodes are arranged adjacent to each other. As a result, the two different linear electrodes can have different resonance frequencies, since they have different lengths. This increases a frequency band used by the wireless IC device.

Preferably, the radiation electrode is a loop-shaped radiation electrode, and an electromagnetic field of the loop-shaped radiation electrode is coupled to electromagnetic fields of the inductance elements included in the functional substrate. As a result, it is possible to strengthen the degree of coupling between the electromagnetic field of the loop-shaped radiation electrode and each of the electromagnetic fields of the inductance elements included in the functional substrate. Furthermore, since a necessary inductance component can be obtained in a relatively small area, it is possible to reduce the size of the wireless IC device. In addition, since the magnetic field of the loop-shaped portion of the radiation electrode is coupled to the magnetic field of the loop-shaped external coupling electrode, it is possible to obtain a predetermined characteristic regardless of the mounting orientation of the functional substrate with respect to the radiation plate.

Preferably, the matching circuit is defined by an element included in the functional substrate and an element mounted on the functional substrate. As a result, it is possible to reduce the size of the functional substrate by mounting a chip inductor having a large inductance value and a chip capacitor having a large capacitance value on the functional substrate so as to reduce the value of the element included in the functional substrate.

Preferably, the wireless IC device further includes a protection film covering at least one of the wireless IC chip, the functional substrate, and the radiation plate. As a result, it is possible to increase the environmental resistance of the wireless IC device and reduce the change in the characteristic of the wireless IC device due to an environmental change.

Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a wireless IC device disclosed in Japanese Unexamined Patent Application Publication No. 2005-244778.

FIGS. 2A and 2B are cross-sectional views of a wireless IC device according to a first preferred embodiment of the present invention and a plan view of a main portion of the wireless IC device.

FIG. 3 is an exploded perspective view of a multilayer substrate included in a functional substrate included in the wireless IC device shown in FIGS. 2A and 2B.

FIG. 4 is an oblique perspective view of a functional substrate on which a wireless IC chip is mounted.

FIG. 5 is an equivalent circuit diagram of the wireless IC device shown in FIGS. 2A and 2B.

FIG. 6 is a plan view illustrating the shape of a radiation electrode provided on a radiation plate used in a wireless IC device according to a second preferred embodiment of the present invention.

FIG. 7 is a plan view illustrating the shape of a radiation electrode formed on a radiation plate used in a wireless IC device according to a third preferred embodiment of the present invention.

FIGS. 8A to 8D are cross-sectional views of main portions of some wireless IC devices according to a fourth preferred embodiment of the present invention.

FIGS. 9A to 9D are cross-sectional views of main portions of some other wireless IC devices according to the fourth preferred embodiment of the present invention.

FIG. 10 is a cross-sectional view of a main portion of a wireless IC device according to a fifth preferred embodiment of the present invention.

FIG. 11 is a cross-sectional view of a main portion of a wireless IC device according to a sixth preferred embodiment of the present invention.

FIG. 12 is a cross-sectional view of a main portion of another wireless IC device according to the sixth preferred embodiment of the present invention.

FIG. 13 is a cross-sectional view of a main portion of a wireless IC device according to a seventh preferred embodiment of the present invention.

FIG. 14 is a cross-sectional view of a main portion of a wireless IC device according to an eighth preferred embodiment of the present invention.

FIG. 15 is diagram illustrating the configuration of a radiation electrode provided on a radiation plate and the shape of a loop-shaped external coupling electrode included in a functional substrate in the wireless IC device.

FIGS. 16A and 16B are impedance circuit diagrams of the wireless IC device shown in FIG. 14.

FIG. 17 is a cross-sectional view of a main portion of a wireless IC device according to a ninth preferred embodiment of the present invention.

FIG. 18 is an impedance circuit diagram of the wireless IC device shown in FIG. 17.

FIG. 19 is a plan view of an electromagnetic coupling module used in a wireless IC device according to a tenth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Preferred Embodiment

A wireless IC device according to the first preferred embodiment of the present invention will be described with reference to FIGS. 2A to 5. FIG. 2A is a cross-sectional view of a main portion of a wireless IC device according to the first preferred embodiment. FIG. 2B is a plan view of the main portion of the wireless IC device.

As illustrated in FIG. 2A, a wireless IC device 300 includes a wireless IC chip 1, a functional substrate 20, and a radiation plate 30. The wireless IC chip 1 is preferably a semiconductor chip including a signal processing circuit functioning as an RFID tag, for example.

The radiation plate 30 includes radiation electrodes 32 a and 32 b provided on the upper surface of a base material 31, such as a PET film, for example.

The functional substrate 20 includes a multilayer substrate 21. On the upper surface of the multilayer substrate 21, mounting electrodes 22 a and 22 b arranged to mount the wireless IC chip 1 are disposed. In the multilayer substrate 21, capacitive coupling electrodes 24 a and 24 b that are capacitively coupled to the radiation electrodes 32 a and 32 b, respectively are provided. The capacitive coupling electrodes 24 a and 24 b are external coupling electrodes of the functional substrate 20. A matching circuit 23 including the capacitive coupling electrodes 24 a and 24 b performs impedance matching between the wireless IC chip 1 and each of the radiation electrodes 32 a and 32 b provided on the radiation plate 30.

The functional substrate 20 is mounted on the radiation plate 30 via an adhesive 40 so that the capacitive coupling electrodes 24 a and 24 b face the internal ends of the radiation electrodes 32 a and 32 b, respectively.

On a surface on which the wireless IC chip 1 is mounted, a soldering bump or an Au bump, for example, is provided so that an underfill is applied in an area between the wireless IC chip 1 and the functional substrate 20 on which the mounting electrodes 22 a and 22 b are provided.

FIG. 2B is a plan view of an area on the upper surface of the radiation plate 30 in which the radiation electrodes 32 a and 32 b are provided. In this drawing, the illustration of the wireless IC chip 1 and the mounting electrodes 22 a and 22 b is omitted. As illustrated in FIG. 2B, the capacitive coupling electrodes 24 a and 24 b included in the functional substrate 20 are arranged so that they occupy two areas that are divided from the functional substrate 20. The radiation electrodes 32 a and 32 b are relatively long. The functional substrate 20 is disposed on the radiation plate 30 so that the capacitive coupling electrodes 24 a and 24 b face the internal ends of the radiation electrodes 32 a and 32 b, respectively.

Thus, the wireless IC chip 1 supplies electric power to the radiation electrodes 32 a and 32 b via the functional substrate 20, so that the radiation electrodes 32 a and 32 b operate as a dipole antenna.

There are several procedures for assembling the wireless IC chip 1, the functional substrate 20, and the radiation plate 30 into the wireless IC device 300. Preferably, a method of creating an electromagnetic coupling module by mounting the wireless IC chip 1 on the functional substrate 20 and mounting the created electromagnetic coupling module on the radiation plate 30 is used. A general method used to mount a semiconductor chip on a substrate can preferably be used for the mounting of the wireless IC chip 1 on the functional substrate 20 having a relatively small size. The electromagnetic coupling module can be easily mounted on the radiation plate 30 having a relatively large size via the adhesive 40.

FIG. 3 is an exploded perspective view of the multilayer substrate 21 included in the functional substrate 20. In this example, the wireless IC chip 1 is also illustrated. The multilayer substrate 21 preferably includes dielectric layers 21 a, 21 b, 21 c, 21 d, 21 e, 21 f, and 21 g. On the dielectric layer 21 a, the mounting electrodes 22 a and 22 b and mounting electrodes 22 c and 22 d, which are used to mount the wireless IC chip 1, are provided. On the dielectric layers 21 b, 21 c, 21 d, 21 e, and 21 f, inductor electrodes 23 a, 23 b, 23 c, 23 d, and 23 e are provided, respectively. On the dielectric layers 21 b, 21 c, and 21 d, inductor electrodes 23 f, 23 g, and 23 h are provided, respectively. On the dielectric layer 21 g, capacitive coupling electrodes 24 a and 24 b are provided. As illustrated in FIG. 3, these dielectric layers are preferably connected to one another by a via hole.

FIG. 4 is an oblique perspective view of the functional substrate 20 on which the wireless IC chip 1 is mounted. The multilayer substrate included in the functional substrate 20 includes an inductor defined by the inductor electrodes 23 a to 23 e and an inductor defined by the inductor electrodes 23 f to 23 h.

FIG. 5 is an equivalent circuit diagram of the wireless IC chip, the functional substrate, and the radiation plate. As illustrated in FIG. 5, the matching circuit 23 included in the functional substrate is preferably defined by the radiation plate, capacitors C1 and C2, and inductors L1 and L2. The inductor L1 represents the inductor defined by the inductor electrodes 23 a to 23 e illustrated in FIGS. 3 and 4. The inductor L2 represents the inductor defined by the inductor electrodes 23 f to 23 h illustrated in FIGS. 3 and 4. The capacitor C1 represents a capacitor defined between the capacitive coupling electrode 24 a and the radiation electrode 32 a. The capacitor C2 represents a capacitor defined between the capacitive coupling electrode 24 b and the radiation electrode 32 b.

An impedance obtained by viewing the wireless IC chip from a connecting portion connecting the wireless IC chip and the functional substrate to each other is represented by R_(IC)+jX_(IC), and an impedance obtained by viewing the radiation electrodes provided on the radiation plate from a connecting portion connecting the functional substrate and the radiation plate to each other is represented by Rant+jXant. For example, assuming that an impedance obtained by viewing the radiation plate (radiation electrodes) from the connecting portion connecting the wireless IC chip and the functional substrate to each other in or near a frequency range such as UHF is R1+jX1, the circuit constant of the matching circuit 23 included in the functional substrate is determined so that the relationship between X_(IC) and X1 is a conjugate relationship, that is, X1=−X_(IC).

The matching circuit 23 included in the functional substrate performs impedance matching between the wireless IC chip and the radiation plate (radiation electrodes). If R_(IC)=R1 is satisfied, that is, the relationship between R_(IC)+jX_(IC) and R1+jX1 is a complex conjugate relationship, the perfect impedance matching between the wireless IC chip and the radiation plate (radiation electrodes) can be achieved. However, in reality, it is difficult for the real parts to be equal or substantially equal to each other (R_(IC)=R1). Accordingly, it is necessary to achieve the conjugate relationship at least between reactive components. In the above-described impedance matching, the consistency between imaginary parts is more important than the consistency between real parts.

Thus, according to the first preferred embodiment, since the capacitive coupling electrodes 24 a and 24 b included in the electromagnetic coupling module obtained by mounting the wireless IC chip 1 on the functional substrate 20 are disposed apart from the radiation plate 30 on which the radiation electrodes 32 a and 32 b are provided, the electromagnetic coupling module is DC-insulated from the radiation electrodes 32 a and 32 b. As a result, an excellent electrostatic discharge (ESD) characteristic can be obtained.

Furthermore, since the matching circuit 23 is included in the functional substrate 20 including the multilayer substrate disposed between the wireless IC chip 1 and the radiation plate 30, that is, since it is not necessary to provide an impedance matching circuit on the side of the radiation plate 30, an area required for the radiation electrodes 32 a and 32 b on the radiation plate 30 can be significantly reduced. As a result, the size of the wireless IC device can be reduced.

Still furthermore, since the matching circuit 23 is included in the multilayer substrate 21, a change in the characteristic of the matching circuit 23 is relatively small, that is, the change in the frequency characteristic of the wireless IC device 300 is relatively small even if the wireless IC device 300 is attached to a product having a high dielectric constant. Accordingly, it is not necessary to design a wireless IC device in consideration of a product to which the wireless IC device is attached. Since the matching circuit 23 is included in the multilayer substrate, it is possible to use a complex matching circuit that cannot easily be provided on a single surface as the matching circuit 23. Accordingly, it is possible to improve the impedance matching and obtain a high-gain wireless IC device.

Second Preferred Embodiment

FIG. 6 is a plan view illustrating an electrode pattern of a main portion on the upper surface of a radiation plate in a wireless IC device according to the second preferred embodiment of the present invention. On the upper surface of the radiation plate, the long radiation electrodes 32 a and 32 b and a matching electrode 34 are provided. The matching electrode 34 connects a portion of the radiation electrode 32 a apart from the internal end of the radiation electrode 32 a by a predetermined distance to a portion of the radiation electrode 32 b apart from the internal end of the radiation electrode 32 b by the predetermined distance.

As in the case illustrated in FIG. 2B, near the internal ends of the radiation electrodes 32 a and 32, the functional substrate 20 is arranged so that the capacitive coupling electrodes 24 a and 24 b included in the functional substrate 20 face the internal ends of the radiation electrodes 32 a and 32 b, respectively. The illustration of the wireless IC chip mounted on the upper surface of the functional substrate is omitted in FIG. 6.

An auxiliary matching circuit portion 35 is defined by the matching electrode 34, and a portion of the radiation electrode 32 a from the internal end of the radiation electrode 32 a to a location connected to the matching electrode 34, and a portion of the radiation electrode 32 b from the internal end of the radiation electrode 32 b to a location connected to the matching electrode 34. Thus, if predetermined portions of the radiation electrodes 32 a and 32 b are connected to each other using the matching electrode 34, the wireless IC chip performs tap feeding so as to supply electric power to a dipole antenna via the functional substrate 20. In an area in which the tap feeding is performed, the auxiliary matching circuit portion 35 performs impedance matching twice, that is, the impedance matching between the functional substrate 20 and the radiation electrode 32 a and the impedance matching between the functional substrate 20 and the radiation electrode 32 b. Accordingly, it is possible to maintain a state in which impedance matching is achieved in a wide frequency band, that is, obtain a high gain in a wide frequency band. While the auxiliary matching circuit portion 35 is provided in the area in which the tap feeding is performed, it is impossible to provide a large inductor on the radiation plate due to limitations of space. Furthermore, it is difficult to provide a capacitor and a circuit in which lines cross each other on the radiation plate. However, if a functional substrate is used, it is possible to provide an inductor, a capacitor, and a circuit in which lines cross each other on the radiation plate. As a result, as described previously, it is possible to maintain a state in which impedance matching is achieved in a wide frequency band, that is, obtain a high gain in a wide frequency band.

Third Preferred Embodiment

FIG. 7 is a plan view illustrating an electrode pattern of a main portion on an upper surface of a radiation plate in a wireless IC device according to the third preferred embodiment of the preferred embodiment. On the upper surface of the radiation plate, a loop-shaped radiation electrode 36 is provided. The loop-shaped radiation electrode 36 is preferably arranged so that both ends thereof face each other and it surrounds a predetermined area. The functional substrate 20 is mounted on the radiation plate so that one end of the loop-shaped radiation electrode 36 faces the capacitive coupling electrode 24 a included in the functional substrate 20 and the other end of the loop-shaped radiation electrode 36 faces the capacitive coupling electrode 24 b included in the functional substrate 20.

As in the first and second preferred embodiments, a module is obtained by mounting the wireless IC chip on the functional substrate 20. The configuration of the functional substrate 20 according to the third preferred embodiment is substantially the same as that of the functional substrates 20 according to the first and second preferred embodiments.

Thus, if the wireless IC chip supplies electric power to the radiation electrodes 32 a and 32 b via the functional substrate 20, the radiation electrodes 32 a and 32 b operate as a magnetic field antenna. As a result, the wireless IC device can communicate with a reader/writer antenna for the wireless IC device using a magnetic field.

Fourth Preferred Embodiment

FIGS. 8A to 8D and 9A to 9D are cross-sectional views illustrating the configurations of some wireless IC devices according to the fourth preferred embodiment of the present invention. The configurations of the radiation plate 30 and the wireless IC chip 1 according to the fourth preferred embodiment are substantially the same as those of the radiation plates 30 and the wireless IC chips 1 according to the first to third preferred embodiments. In the fourth preferred embodiment, some examples of a matching circuit included in a functional substrate will be described.

In an example illustrated in FIG. 8A, a matching circuit is defined by the inductors L1, L2, an inductor L3, and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 120. In the example illustrated in FIG. 5, the mounting electrode 22 b is through-connected to the capacitor C2. In the matching circuit according to the fourth preferred embodiment, the inductor L3 is disposed at the through-connection portion. Accordingly, it is possible to reduce the inductance values of the inductors L1 to L3 and easily provide the inductors L1 to L3 in a multilayer substrate.

In an example illustrated in FIG. 8B, a matching circuit is defined by the inductors L1 and L3, and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 121. In this example, a shunt inductor is not disposed between the capacitive coupling electrodes 24 a and 24 b. Accordingly, it is possible to easily convert a small impedance. That is, if the above-described shunt inductor has a small inductance value, it significantly changes the impedance of an impedance matching circuit. In this example, since such a shunt inductor is not used, such a problem does not arise.

In an example illustrated in FIG. 8C, a matching circuit is defined by the inductor L3 and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 122. In this example, since only the inductor L3 is used, it is possible to achieve the easy configuration of the matching circuit.

In an example illustrated in FIG. 8D, a matching circuit is defined by inductors L11, L12, L21, L31, and L32 and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 123. In this example, since the inductors L12 and L32 are included, the inductance values of the radiation electrodes 32 a and 32 b can be reduced. Accordingly, the size of the radiation electrodes can be reduced.

In an example illustrated in FIG. 9A, a matching circuit is defined by the inductors L21, L31, and L32 and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 124. In this example, since the inductors L11 and L12 illustrated in FIG. 8D are removed, it is possible to provide an easy configuration of the matching circuit while enabling the matching circuit to have the characteristic illustrated in FIG. 8D.

In an example illustrated in FIG. 9B, a matching circuit is defined by the inductors L11, L21, and L32 and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 125. In this example, the location of the inductor L31 illustrated in FIG. 9A is changed. Accordingly, it is possible to provide easy wiring in the multilayer substrate while enabling the matching circuit to have the same or substantially the same effect as that illustrated in FIG. 9A.

In an example illustrated in FIG. 9C, a matching circuit is defined by capacitors C11 and C31, inductors L22 and L23, and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 126. In this example, since the matching circuit includes the capacitors C11 and C31 connected in series to each other, it is possible to achieve the impedance matching between each of the radiation electrodes (antenna) having a capacitive impedance and the wireless IC chip 1 having a capacitive impedance in a wide frequency range.

In an example illustrated in FIG. 9D, a matching circuit is defined by the inductors L22 and L23, the capacitor C31, and the capacitive coupling electrodes 24 a and 24 b in a functional substrate 127. In this example, since the capacitors C11 and C31 illustrated in FIG. 3C are integrated into the capacitor C31, it is possible to achieve easy pattern formation in the multilayer substrate while enabling the matching circuit to have the same or substantially the same effect as that illustrated in FIG. 9C.

The circuit constant of each of the matching circuits included in the functional substrates 120 to 127 is preferably determined so that the relationship between the reactive component of an impedance obtained by viewing the wireless IC chip from the connecting portion connecting the wireless IC chip and the functional substrate to each other and the reactive component of an impedance obtained by viewing the radiation electrodes from the connecting portion connecting the wireless IC chip and the functional substrate to each other is a conjugate relationship. Thus, a matching circuit including at least one inductance element and at least one capacitance element as required.

Fifth Preferred Embodiment

FIG. 10 is a cross-sectional view of a main portion of a wireless IC device according to the fifth preferred embodiment of the present invention. As illustrated in FIG. 10, the wireless IC chip 1 is mounted on the upper surface of the functional substrate 20, and the wireless IC chip 1 is covered with a resin 41 on the upper surface of the functional substrate 20 so that a flat upper surface is obtained. Other configurations are substantially the same as those described in the first preferred embodiment.

Thus, when an electromagnetic coupling module obtained by mounting the wireless IC chip 1 on the functional substrate 20 is mounted on the radiation plate 30, it is possible to easily grasp the electromagnetic coupling module by suction and chuck the electromagnetic coupling module on the radiation plate 30. Since the wireless IC chip 1 is embedded in the resin 41, the environmental resistance of the wireless IC chip 1 is increased.

A protection film may preferably be arranged on not only the wireless IC chip 1 but also on the functional substrate 20 or the radiation plate 30. Alternatively, a protection film may preferably be arranged so as to cover all of the wireless IC chip 1, the functional substrate 20, and the radiation plate 30. This is also true for other preferred embodiments of the present invention.

Sixth Preferred Embodiment

FIGS. 11 and 12 are cross-sectional views of main portions of wireless IC devices according to the sixth preferred embodiment of the present invention. In an example illustrated in FIG. 11, a functional substrate 128 includes the multilayer substrate 21, and capacitive coupling electrodes 224 a and 224 b are arranged so that they are exposed at the undersurface of the multilayer substrate 21.

The capacitive coupling electrodes 224 a and 224 b face the internal ends of the radiation electrodes 32 a and 32 b, respectively, via the adhesive 40. As a result, a large capacitance can be generated between the capacitive coupling electrode 224 a and the internal end of the radiation electrode 32 a and between the capacitive coupling electrode 224 b and the internal end of the radiation electrode 32 b.

In an example illustrated in FIG. 12, each of external coupling electrodes 225 a and 225 b is arranged so as to extend from the undersurface to the side surface of a functional substrate 129. The coupling electrodes 225 a and 225 b are preferably connected to the radiation electrodes 32 a and 32 b, respectively, via a conductive joining material 42, such as solder, for example.

As a result, it is possible to achieve the direct electrical connection between the coupling electrode 225 a included in the functional substrate 129 and the radiation electrode 32 a provided on the radiation plate 30 and the direct electrical connection between the coupling electrode 225 b included in the functional substrate 129 and the radiation electrode 32 b provided on the radiation plate 30. Furthermore, it is possible to increase the mechanical strength of the wireless IC device by increasing a solder connecting area.

Seventh Preferred Embodiment

FIG. 13 is a cross-sectional view of a main portion of a wireless IC device according to the seventh preferred embodiment of the present invention. Referring to FIG. 13, a multilayer substrate is included in a functional substrate 220. The multilayer substrate includes inductance electrodes and capacitive coupling electrodes. On the upper surface of the multilayer substrate, a chip inductor 51 that is preferably a discrete component is mounted. A matching circuit is defined by the internal electrodes included in the functional substrate 220 and the external chip component.

In a wireless IC device having the above-described configuration, it is possible to reduce the size of the functional substrate by mounting a chip inductor having a large inductance value or a chip capacitor having a large capacitance value on the functional substrate so as to reduce the inductance or capacitance value of an element included in the functional substrate.

Eighth Preferred Embodiment

A wireless IC device according to the eighth preferred embodiment of the present invention will be described with reference to FIGS. 14 to 16B. FIG. 14 is a cross-sectional view of a main portion of a wireless IC device according to the eighth preferred embodiment. In a radiation plate 130, the radiation electrodes 32 a, 32 b, and 32 c are provided on the upper surface of the base material 31. A functional substrate 221 includes a loop-shaped external coupling electrode 226. An electromagnetic coupling module obtained by mounting the wireless IC chip 1 on the functional substrate 221 is mounted on the radiation plate 130 so that the magnetic field of the loop-shaped external coupling electrode 226 and the magnetic field of the radiation electrode 32 c are coupled to each other.

FIG. 15 is a plan view of radiation electrodes provided on the upper surface of the radiation plate 130 and a loop-shaped external coupling electrode included in the functional substrate 221. The radiation electrodes 32 a and 32 b, which are relatively long, are connected to each other by the loop-shaped radiation electrode 32 c. The loop-shaped external coupling electrode 226 included in the functional substrate is preferably spirally wound with a plurality of turns and a size that is about the same as the loop-shaped radiation electrode 32 c.

Thus, the winding axis of the loop-shaped external coupling electrode 226 that is an inductance element that is spirally wound with a plurality of turns crosses an area in which the radiation electrode 32 c is provided. As a result, a magnetic field is generated at the loop-shaped external coupling electrode 226 in a direction that is parallel or substantially parallel to the winding axis and is vertical or substantially vertical to the radiation electrode 32 c, and a magnetic field is generated around (in and out of) the radiation electrode 32 c. Accordingly, a magnetic field loop generated at the functional substrate 221 is interlinked with a magnetic field loop generate at the radiation electrode 32 c, so that the degree of coupling between the loop-shaped external coupling electrode 226 and the radiation electrode 32 c can be further increased.

In the examples illustrated in FIGS. 14 and 15, the loop-shaped radiation electrode 32 c is provided. However, instead of a loop-shaped radiation electrode, for example, a dipole electrode may preferably be used as the radiation electrode 32 c. Such a dipole electrode can also be strongly coupled to the loop-shaped external coupling electrode 226, since the magnetic flux of the loop-shaped external coupling electrode 226 passes around the radiation electrode 32 c and is then coupled to the magnetic field of the radiation electrode 32 c.

Furthermore, in the examples illustrated in FIGS. 14 and 15, the loop-shaped external coupling electrode 226 that is spirally wound is provided. However, a loop-shaped external coupling electrode that is wound with a single turn may preferably be used as the loop-shaped external coupling electrode 226.

FIGS. 16A and 16B are impedance circuit diagrams of the above-described wireless IC chip, the above-described functional substrate, and the above-described radiation plate. Referring to FIG. 16A, an inductor La on the side of the radiation plate is an inductor at the radiation electrode 32 c, and an inductor Lb on the side of the functional substrate is an inductor at the loop-shaped external coupling electrode 226. One terminal of the wireless IC chip 1 is connected in series to an inductor Lc.

If the mutual inductance between the inductors La and Lb between which a magnetic field coupling is achieved is represented by M, the circuit illustrated in FIG. 16A can be changed to a circuit illustrated in FIG. 16B. The inductors La, Lb, and Lc illustrated in FIG. 16A are determined so that the relationship between X_(IC) and X1 illustrated in FIG. 16B is a conjugate relationship.

Thus, since a matching circuit includes the inductor at the radiation electrode 32 c, the impedance matching between an antenna defined by the radiation electrodes 32 a and 32 b and the wireless IC chip can be achieved.

According to the eighth preferred embodiment, since both of the radiation electrode 32 c on the side of the radiation plate and the loop-shaped external coupling electrode 226 on the side of the functional substrate are loop-shaped electrodes, the mounting direction of the module, which is obtained by mounting the wireless IC chip 1 on the functional substrate 221, with respect to the radiation plate 130 has substantially no effect on the characteristics. That is, if the module is mounted on the radiation plate 130 in any orientation, a predetermined characteristic can be obtained.

Ninth Preferred Embodiment

FIG. 17 is a cross-sectional view of a main portion of a wireless IC device according to the ninth preferred embodiment of the present invention. In this example, a functional substrate 222 includes a double helix external coupling electrode 227. The magnetic field of the double helix external coupling electrode 227 and the magnetic field of the loop-shaped radiation electrode 32 c provided on the radiation plate 130 are coupled to each other.

The double helix external coupling electrode 227 has a double helix configuration in which two different linear electrodes are adjacent to each other and ends of these linear electrodes are electrically connected to each other. The pattern of the radiation electrodes provided on the radiation plate 130 is substantially the same as that illustrated in FIG. 15.

FIG. 18 is an impedance circuit diagram of the wireless IC chip illustrated in FIG. 17. Inductors Lb1 and Lb2 included in a functional substrate are inductors at the double helix external coupling electrode 227. Capacitors Ca and Cb are capacitors included in the multilayer substrate included in the functional substrate 222. The inductor La at a radiation substrate is an inductor at the loop-shaped radiation electrode 32 c. The magnetic field of the inductor La is coupled to the magnetic fields of the inductors Lb1 and Lb2 at the double helix external coupling electrode.

The constants of circuit elements of the matching circuit included in the functional substrate are determined so that the relationship between a reactance component X_(IC) of an impedance obtained by viewing the wireless IC chip from a connecting portion connecting the wireless IC chip and the functional substrate to each other and a reactance component X1 of an impedance obtained by viewing the radiation electrodes 32 a and 32 b from the connecting portion connecting the wireless IC chip and the functional substrate to each other is a conjugate relationship.

Thus, by using an external coupling electrode having a double helix shape, the degree of coupling between the external coupling electrode and a radiation electrode can be increased. Furthermore, since the two lines included in the double helix external coupling electrode have different lengths, the two lines can have different resonance frequencies. Accordingly, it is possible to increase a frequency band used by the wireless IC device.

Tenth Preferred Embodiment

FIG. 19 is a plan view illustrating the configuration of a functional substrate used in a wireless IC device according to the tenth preferred embodiment of the present invention. In this example, an electrode pattern is provided on only the upper surface of a functional substrate 223. As illustrated in FIG. 19, a double helix external coupling electrode 228 is provided on the upper surface of the functional substrate 223, and the inner ends of the double helix external coupling electrode 228 define the mounting electrodes 22 a and 22 b for the wireless IC chip 1. Other mounting electrodes 22 c and 22 d are provided near the mounting electrodes 22 a and 22 b. An electromagnetic coupling module is obtained by mounting the wireless IC chip 1 on the mounting electrodes 22 a to 22 d.

The configuration of a radiation electrode on the side of a radiation plate is substantially the same as that illustrated in FIG. 15. The electromagnetic coupling module illustrated in FIG. 19 is preferably arranged so as to face the loop-shaped radiation electrode 32 c as illustrated in FIG. 15. As a result, the double helix external coupling electrode 228 is electromagnetically coupled to the loop-shaped radiation electrode 32 c. Thus, an impedance matching circuit can be obtained without using a multilayer substrate.

In the above-described preferred embodiments, various typical examples of a wireless IC device have been described. However, a wireless IC device may be obtained by combining configurations described in any of the above preferred embodiments.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A wireless IC device comprising: a wireless IC chip; a radiation plate including a radiation electrode; and a functional substrate including a matching circuit arranged to perform impedance matching between the wireless IC chip and the radiation electrode, the functional substrate including a coupling electrode coupled to the radiation electrode, inductance elements, and a capacitance element; wherein the matching circuit included in the functional substrate has a configuration such that a relationship between a reactance component of an impedance obtained by viewing the wireless IC chip from a connecting portion connecting the wireless IC chip and the functional substrate to each other and a reactance component of an impedance obtained by viewing the radiation electrode from the connecting portion connecting the wireless IC chip and the functional substrate to each other is a conjugate relationship.
 2. The wireless IC device according to claim 1, wherein the coupling electrode is electromagnetically coupled to the radiation electrode.
 3. The wireless IC device according to claim 1, wherein the functional substrate includes a multilayer substrate including laminated dielectric layers on which electrode patterns are provided.
 4. The wireless IC device according to claim 1, wherein the radiation electrode has an elongated configuration; the coupling electrode includes first and second external coupling electrodes that individually occupy two areas divided from the functional substrate; and one end of the radiation electrode is coupled to the first external coupling electrode and another end of the radiation electrode is coupled to the second external coupling electrode.
 5. The wireless IC device according to claim 4, wherein the radiation electrode is a loop-shaped radiation electrode arranged such that both ends of the radiation electrode face each other; a first one of the both ends of the radiation electrode is coupled to the first external coupling electrode; and a second one of the both ends of the radiation electrode is coupled to the second external coupling electrode.
 6. The wireless IC device according to claim 4, further comprising an auxiliary matching circuit portion including a matching electrode arranged to connect a location near the first one of the both ends of the radiation electrode to a location near the second one of the both ends of the radiation electrode, a portion of the radiation electrode extending from the first one of the both ends of the radiation electrode to a location near the one of the both ends of the radiation electrode, and a portion of the radiation electrode extending from the second of the both ends of the radiation electrode to a location near the second of the both ends of the radiation electrode.
 7. The wireless IC device according to claim 1, wherein the inductance elements are loop-shaped inductance elements; and winding axes of the loop-shaped inductance elements are arranged so that they cross an area in which the radiation electrode is located.
 8. The wireless IC device according to claim 1, wherein the coupling electrode is a capacitive coupling electrode that faces the radiation electrode and is capacitively coupled to the radiation electrode.
 9. The wireless IC device according to claim 8, wherein the capacitive coupling electrode is provided on a surface of the functional substrate facing the radiation plate; the radiation electrode is provided on a surface of the radiation plate facing the functional substrate; and the functional substrate is attached to the radiation plate so that the capacitive coupling electrode and the radiation electrode face each other.
 10. The wireless IC device according to claim 8, wherein the external coupling electrode included in the functional substrate extends to a surface other than the surface of the functional substrate facing the radiation plate.
 11. The wireless IC device according to claim 1, wherein the coupling electrode is a loop-shaped external coupling electrode; and the loop-shaped external coupling electrode is magnetically coupled to the radiation electrode.
 12. The wireless IC device according to claim 11, wherein at least one of the inductance elements has a double helix shape in which two different linear electrodes are adjacent to each other; and one end of one of the two different linear electrodes is electrically connected to one end of the other one of the two different linear electrodes.
 13. The wireless IC device according to claim 11, wherein the radiation electrode is a loop-shaped radiation electrode; and the loop-shaped radiation electrode is electromagnetically coupled to the inductance elements included in the functional substrate.
 14. The wireless IC device according to claim 1, wherein the matching circuit includes an element included in the functional substrate and an element mounted on the functional substrate.
 15. The wireless IC device according to claim 1, further comprising a protection film covering at least one of the wireless IC chip, the functional substrate, and the radiation plate. 